Discovery of NIRF theranostic probes targeting amyloid-β and cholinesterases in Alzheimer's disease models.

Alzheimer's disease (AD) remains a major unmet medical challenge, with limited tools that integrate early diagnosis and therapeutic intervention. Considering the pivotal roles of amyloid-β (Aβ) and cholinesterases (ChEs) in AD etiology, we report dual-functional theranostic NIR-I probes. The lead candidate, I-43, exhibits favorable NIR optical properties (Stokes shift ≥ 220 nm) and binds strongly to Aβ fibrils, with Kd values of 58.2 ± 9.7 nM for Aβ1-40 and 104 ± 25 nM for Aβ1-42. Histological staining of brain tissues from transgenic APP-PS1 mice and human autopsy samples confirms selective detection of Aβ plaques with a high signal-to-noise ratio and minimal cross-reactivity toward pathogenic tau tangles and α-synuclein. In addition, I-43 exhibits fluorescence response toward AChE, shows inhibitory activity (IC50 = 0.38 µM), and enhances memory in a scopolamine-induced amnesia in Swiss albino mice. Despite this, limited aqueous solubility and metabolic stability necessitate structural modifications and formulation strategies to broaden the scope in preclinical studies. Herein, we demonstrate that probes can be engineered to label key AD biomarkers with ChEs inhibitory activity, paving the way to an alternate theranostic approach in AD management.